How do PUR Hotmelt Adhesives Work?

PUR adhesives are reactive polyurethane hot melt adhesives. They are one-part synthetic specialty adhesives with the strength of structural adhesives, but with the application speed of hotmelts. Similar to regular hotmelts, PUR adhesives are heated until they reach a liquid state, applied to your substrates, and the bond is created as the adhesive cools. However, where PUR adhesives differ, is that they react with the moisture in the air and continue to cure over the next 24-48 hours, providing a much stronger bond than traditional hotmelts.

PUR hotmelts come in the form of a cartridge or a slug, and because of their reactive properties, must be heated and applied by special PUR hotmelt equipment. Depending on the application, they can be either sprayed or extruded, with guns or bulk dispensing equipment. Guns are used for smaller applications and are more affordable and easy to use. Bulk equipment is used for automated or high volume dispensing applications, but is more expensive, harder to use, and provides less movement and application freedom.

PUR adhesives are used in applications where high strength and plasticizer resistance is needed, for permanent applications, and for difficult-to-bond substrates. They can bond many substrates including wood, fabrics, leather, metals, glass, ceramics, and some plastics such as polystyrene and polyacrylic. These adhesives are used in many applications across many industries including automotive, filter, door, window and floor manufacturing, textile and panel assembly, woodworking and edgebanding, home repair, bookbinding and even packaging applications.

However, PUR adhesives also have some major drawbacks, so we’ve listed all their pros and cons in the table below.

Pros: PUR Adhesives

Cons: PUR Adhesives

  • Not just a thermal bond, but an actual chemical change – resulting in a much stronger bond
  • Resistant to temperature extremes
  • Versatile
  • Easy to dispense – no mixing required
  • Rapid handling strength and high final strength
  • Creates a flexible bond, providing vibration and impact resistance
  • Chemical-resistant
  • Adheres difficult-to-bond, nonporous substrates
  • Suitable for indoor and outdoor use
  • High-strength bonds can be made using less adhesive than other hot melt glues
  • Significantly stronger than traditional hot melt adhesives
  • Low VOCs compared to traditional hot melt materials
  • Contains isocyanates, which are poisonous
  • Cannot be exposed to air or moisture before use, otherwise will cure prematurely and become unusable
  • Must be packaged in airtight cartridges or foil to prevent exposure
  • Shelf life is around 12 months, compared to traditional hot melts which have an indefinite shelf life
  • Requires expensive, specialized equipment
  • Bulk equipment must be cleaned and purged regularly, as adhesive is very difficult to remove once cured
  • Can create a noticeable bond line which can look unappealing and can negatively impact the quality of the finished product
  • It is imperative to get the application right the first time, as there’s only a short window of time to make adjustments before the adhesive cures
  • Is less “forgiving” than other types of adhesives, if you don’t get the exact result you want the first time you may need to start over

Curious to know what type of adhesive is best for your application? Contact us and let us know your application and the substrates you’re bonding – we would love to provide our recommendations!

Want to learn more about regular hotmelts? Check out one of these blogs:

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